1. Field of the Invention
This invention relates to a solar battery and a process for producing the same, particularly to a solar battery which has a good energy conversion efficiency and can be formed with excellent productivity over a large area and a process for producing the same.
2. Related Background Art
In various instruments, solar batteries have been utilized as the driving energy source.
Solar batteries use a p-n junction for the functional portion and silicon is generally employed as the semiconductor material constituting the p-n junction. Although it is preferable to use single crystalline silicon with respect to efficiency to convert photoenergy to electromotive force, amorphous silicon has been deemed to be more advantageous with respect to enlargement of area and reduction in cost.
In recent years, use of polycrystalline silicon has been investigated for the purpose of obtaining low cost comparable to amorphous silicon and high energy conversion efficiency comparable to single crystalline silicon. Whereas, according to the method proposed in the prior art, a mass of polycrystalline silicon has been sliced into a plate for use, and therefore it was difficult to make the thickness 0.3 mm or less, whereby the dose of light to reach the p-n junction cannot be sufficiently ensured and the energy conversion efficiency was not sufficient in this respect. Thus, it is required to make the thickness thinner for enhancement of the efficiency.
Accordingly, it has been attempted to form a thin film of polycrystalline silicon by utilizing a thin film forming technique such as chemical vapor deposition (CVD) method, etc., but the crystal grain size can become at most some hundredth microns, and the energy conversion efficiency is lower even when compared with the mass polycrystalline silicon slicing method.
Also, it has been attempted to enlarge the crystal grain size by melting the polycrystalline silicon thin film formed according to the above CVD method by irradiation with a laser beam followed by recrystallization. However, this method is not satisfactory in reduction of cost and also stable production can be done only with difficulty.